I've been looking at the guidelines on setting up disk drives to use Adobe and it seems common practice to put "Previews, Media Cache, Exports" all on the same drive.

Question1: If I set my Cache Disk to this in the Preferences, does it take care of sending all these things to the one hard drive or do I have to in every Adobe program specify location for Previews, one for Media Cache, and one for Exports?

Question2: How big of a drive is reasonable to use only for "Previews, Media Cache, Exports"?

Previews and Cache on the same drive is OK, but you'll get slowed down if Exports are also on that drive. Best to separate them.

That statement is overdone, the impact is marginal, especially if one is starved for disks. If you have a limited number of disks available, you have to compromise. It is better to have a dedicated disk for each of your cameras, than putting all that source material on a single disk. That requires more disks and quickly loses the capability to have a dedicated export drive.

Why? Well, quite simply you generally spend days if not weeks editing and every speed gain you have during that period is worthwhile. You only export once and what does it matter if your export takes 2 minutes longer? Also keep in mind that during export the previews and conformed audio and PEK files are not used, unless you specifically tick the Use Previews box, which generally is not advised.

If you have a limited number of disks available, you have to compromise.

Agreed. But I feel Scratch and Cache are better off on the Project drive than the Export drive.

during export the previews and conformed audio and PEK files are not used

Conformed audio is. (Or at least, it should be. The whole benefit of conforming is to get a 32 bit floating point for editing, very handy when audio effects are used. I'd hate to think PP goes back to the original audio for export. If it does, then creating the conformed files in the first place seems kind of a waste.)

I am also interested in what would you do if you had 2 disks (plus OS disk).

Here's the ideal hierarchy that I recommend.

C: System (Windows and Programs)

D: Media

E: Exports

F: Projects

G: Cache

H: Scratch

I: Images (from Encore as Masters)

You move items up if you don't have the drive. For example, if you don't have the I: drive, you put Images on the Scratch disk. If you don't have H; you put Images and Scratch on the Cache disk. If you don't have G: you put Images, Scratch and Cache on the Project drive. Etc. This keeps the load spread out as efficiently as possible for any given number of disks.

Two 2TB drives as a RAID0 for cache. I put my Windows paging file on here also.

One 2TB drive for finished product, the My Documents folders and all of my editing resources like lower thirds, backgrounds, etc.

You could reduce the drive size to 1TB or less to save money and get the same results.

I am tied for third place in the Disk I/O category on http://PPBM5.com among CS6 users. (#2 ranking of all CS6 users) So, while I like Jim's idea of even more disks for all of the different categories of storage requirements (using RAID0 for media and cache like I do) there is a limit to how much money most people have. Mine works great. I don't see a bottleneck (except with RED footage which would force a different RAID configuration and a lot more space if I ever had to use it for more than a quick test). I should point out that my drives are pretty empty. And brand new. It helps with the spped.